An ATP stimulated DNA-synthesizing complex can be isolated from E. coli. Our best evidence indicates the complex is composed of DNA polymerase I and the recBC enzyme (exonuclease V). We are attempting to synthesize the complex in vitro from purified DNA polymerase I and exonuclease V. Although there are indications that this can be achieved, many rigorous controls must be performed to prove that, in fact, a complex has been synthesized and that it is the same as the biological one.